Snakebite in Sri Lanka

Sri Lanka, though an island of relatively small size, is the richest country in herpetological wealth in South Asia. Her rich and diverse herpetofauna consists of approximately 100 amphibian and 190 reptile species. Of these two groups nearly 60% species are endemic. Of the reptiles, 96 species are snakes. In Sri Lanka the annual death rate due to snakebite envenoming is one of the highest in the world being 6 in 100,000 population. Important factors which contribute to this high incidence of snakebite morbidity and mortality are: the presence of representatives of all the known snake families which contain venomous species (Colubridae, Elapidae, Hydrophiidae and Viperidae), the favorable climates and habitats, the socio-economic condition of the people, the preference of some victims for seeking traditional treatment for snakebite instead of western management (antivenom), clearing and alterations to the natural vegetation and habitats by people for settlements, agriculture and plantations.

The present paper is an attempt to show that the habits of snakes, the environment, the socio-economic status of the victim, and the type of treatment adopted have a direct influence on the incidence of snakebite morbidity and mortality in Sri Lanka.

The Climatic or ecological zones

Three distinct climatic zones based on rainfall and vegetation is present; namely wet, dry and intermediate. The dry, wet and the intermediate climatic zone constitute 65%, 23% and 12% respectively of the island's total land area (IIED, 1992).

Physiographic

Three peneplains or erosion levels are recognized. The lowest or the first peneplain is the largest and ranges from sea level to 270m. The second or the uplands with elevations from approximately 270 to 1060 m occupy nearly three-tenths of the island. The highlands or the third peneplain has elevations of 910 to 2420 m. (Wadia, 1945 and Vitanage, 1972).

Vegetation

The island possesses a rich flora consisting of nearly 3500 species of vascular plants. Sri Lanka is primarily an agricultural country; and has been for the past 10,000 years BP. As a result, over the years many natural ecosystems have been transformed into agro-ecosystems. Highly venomous snakes such as the cobra, Russell's viper, kraits are common in these agro-ecosystems.

Forests

The forests are divided into four types (IIED, 1992). They are:

a) The tropical wet evergreen forests, situated at altitudes below 1,000 m in the low country of the wet zone. They are fragile and least resistant to disturbance;

c) Tropical humid and semi-evergreen forests of the intermediate zone, which have virtually disappeared except for degraded patches at Barigoda (near Kurunegala);

d) Tropical dry mixed evergreen forests, which have developed in the dry zone over the past 500-800 years.

The natural physical environment discussed above is the key factor which also determines the distribution of snakes (de Silva, 1981, 1987, 1990, 1992) and other reptiles (de Silva, 1996, 2005). In fact recent analysis of the distribution of the flora and fauna of the island shows its relationships to climate, vegetation and altitude (Crusz 1984, Gunatilleke et al. 1995, Senanayake et al. 1977).

Typical examples of the influence of climate and vegetation in the distribution of snakes are: the two species of kraits that inhabit Sri Lanka: Bungarus ceylonicus (Ceylon or Sri Lanka krait) inhabits the wet and intermediate climatic zones from 30 m up to 2000 m above the mean sea level and Bungarus caeruleus (Common krait) is mainly confined to the dry zone plains up to about 300 m.

Aquatic

Sri Lanka possesses three hectares of inland waters for every square kilometer of land. This is one of the highest densities of inland lakes, ponds, man made canals and still waters in the world (Baldwin, 1991). The coastal waters around the island are warm and many coastal lagoons and estuaries are present.

THE BIOLOGICAL ENVIRONMENT

In this paper, the term biological environment embraces: 1) snakes, 2) the prey animals of snakes, and 3) humans.

Snakes

The snake fauna of Sri Lanka is diverse and range from the primitive uropeltids to the modern viperids. Ninety six species of snakes are recorded from Sri Lanka (Das, 1996, de Silva, 1990, 2001), of which fifty one (53%) are endemic to the island. Nine species are geographic relicts. Of the Sri Lankan snakes, 32 species are considered medically important as they possess either the venom or Duvernoy's glands (which produce venom) and an efficient fang system (especially in the solenoglyphous vipers) to deliver the venom during a bite. Depending on the species of snake, the signs and symptoms manifested in an envenomed human may vary from mild local reactions to systemic envenoming, even ending in death.

Venomous snakes

The following venomous snakes are responsible for a high incidence of snakebite morbidity and mortality in Sri Lanka: Cobra (Naja naja), Common krait (Bungarus caeruleus), Sri Lanka krait (Bungarus ceylonicus), Russells's viper (Daboia russelii), Saw scale viper (Echis carinatus), Hump nose viper (Hypnale hypnale), Green pit viper (Trimeresurus trigonocephalus), and approximately the 13 species of marine snakes which inhabit the coastal waters and estuaries around the island. Their morphological features, habits, habitat, distribution, defense and action of venom together with colour illustrations have been published by de Silva, 1990. Sea snakes have been dealt separately (de Silva, 1989, 1993, Golay et al 1993).

Recent observations indicate that bites by some non venomous and aglyphous snakes too are able to produce from mild local reactions to transient mild systemic poisoning (Kularatne & de Silva, 1997). The aglyphous and non venomous Python molurus, too is considered a medically important snake as it can inflict a bite causing severe lacerations or could even kill a human by asphyxiation by tightening its coils around the thoracic region of the victim. Nevertheless, snakes are an ecologically important group of animals in our ecosystems, adding to the biodiversity of the country. Their venoms are valuable natural substances in research .

Morphology

Most venomous snakes have cryptic coloration, and thus blend with or simulate some inanimate object of the environment, thus increasing the chances of treading on them. This is especially evident in vipers, and is perhaps a good reason for the high incidence of viperine bites. A typical example is Hypnale species. The brown, grey and black cryptic coloration of Hypnale camouflages it well amongst dry fallen leaves and other vegetation on the ground. Its resting coiled posture of its body and holding its head elevated at an angle of 45º resembles a dry curled leaf (mainly rubber, coffee or cashew (Anacardum occidentale L.) plantations where Hypnalehypnale is common. The brown, grey, black, brick red and white coloration of the Russell's viper (Daboia russelii) and Echis carinatus helps them to merge well with the soil, dry vegetation, rocks and logs where the two species rest during the day. Similarly, the green, yellow and black colour of the Green pit viper

(Trimeresurus trigonocephalus) merges into the foliage of the trees, shrubs and creepers on which they rest, resulting in a fair number of people being bitten by green pit vipers while plucking tea leaves, clearing forests and weeding.

Sex

The female population of some venomous snakes such as Hypnale hypnale is high: in one study where 53 were sexed, 37 (70 %) were females (de Silva, 1988). Gloyd and Conant (1990) state that of "more than 100 specimens examined, females outnumber males by more than two to one". In two clutches consisting of 8 and 5 healthy Hypnale hypnale hatchlings, 6 (75%) and 3 (60%) were females respectively. Hypnale produce an average of 7 (range 3-18) young in a clutch (de Silva & Toriba, 1984, de Silva 1988). This could be a reason for Hypnale hypnale to be common, resulting in a high incidence of bites.

Adaptability of snakes

The nocturnal and secretive nature of many venomous snakes, such as Daboia russelii, Bungaruscaeruleus, Bungarus ceylonicus, Hypnale hypnale helps them adapt to life in agricultural fields, farmlands and in proximity to human dwellings in rural and urban areas, even in city environments.

Food habits and prey animals

Rats, which come into paddy fields to feed on grain attracts vipers, cobras and other snakes. This is especially evident during harvesting time when the water from the fields are drained. Whitaker and Dattatri (1986) in a scat analysis of captured wild Indian snakes have shown that 85 % of 53 cobras, 71% of 24 Russell's vipers, 29% of 69 common kraits, and 22% of 160 saw-scale vipers, contained remnants of rodents in their scat. In Sri Lanka, several Russell's vipers received by me contained field rats in their stomachs (Oshea, de Silva & Kularatne, 2 ..).

The following prey animals of snakes are common in human habitations, agricultural fields, and plantations facilitating snake/human contact. Some of these animals are: frogs (Fejervarya limnocharis, Fejervarya kirtisinghei, both species so common in paddy (rice) fields that they are called paddy field frogs), field mice (Mus booguda), house rats (Rattus rattus), house mice (Mus musculus), field rats (Millardia meltada), house geckos (Gehyra multilata, Hemidactylus frenatus, Hemidactylusbrookii etc) skinks (such as Mabuya, Riopa, Lankascincus,), land monitor lizards (Varanus bengalensis), house sparrows and poultry.

In May, 1997, in Anuradhapura, a large cobra (1.5 m) had climbed a thatched roof in which a 75 cm long monitor lizard (Varanus bengalensis) used to spend the night. The cobra had caught the lizard around 2100 hours, and in the struggle, which ensued both, had fallen on a man sleeping below. In the excitement, the cobra had bitten the man's leg. Along with the patient, the killed cobra too was brought to the hospital. The man had to undergo surgery for extensive necrosis of the leg. Some prey animals, such as skinks (Mabuya, Lankascincus and Lygosoma species) which are commonly found near houses have a curious habit of getting on to beds in the night and creeping under pillows, mattresses or bed sheets. I have observed this behavior many times, including one Mabuya madarazi sleeping under my pillow.

Habits

The following habits of snakes contribute to the high incidence of snakebite in Sri Lanka:

a) Reproductive period:

Increased activity of Bungarus caeruleus and Bungarus ceylonicus males was observed during their mating season (September, October, November), contributing to a rise in the incidence of krait bites (de Silva, 1986, 1992). A majority (89%) of known Bungarus caeruleus bites were inflicted by males (de Silva, 1992).

b) Frequenting of roads

Many species of snakes, such as Daboia russelii, Bungarus caeruleus and non venomous Elaphehelena, Oligodon arnensis come on to roads at dusk or night specially immediately after rain, increasing the chances of people being bitten. Epidemiological studies have shown that 15% of snakebites had been inflicted on roads (de Silva & Ranasinghe, 1983). Furthermore, when many drivers attached to various development schemes were interviewed, they related with "pride" the number of Russell's vipers they had run over and killed.

c) Monsoon rains

Reptiles and amphibians become active immediately after showers or during monsoon rains (September, October, and November) in the dry zone. Activities of amphibians and reptiles are stimulated by high humidity and by rain. In fact, most krait bites are preceded by rain even in other months. In Anuradhapura hospital, it has become the practice in the intensive care unit, to keep a bed vacant in anticipation of a krait bite patient if the Meteorological Department forecasts rainy weather (S. A. M. Kularatne, in litt.).

d) Manner of biting

It was observed that the biting manner of snakes influences the degree of envenoming: Bungarus caeruleus chews on the site of the bite, and often the snake had to be pulled away while biting (de Silva, 1992) hence, appreciable amounts of venom could be injected. In the cobra, the majority of bites were defensive "dry bites", which resulted most times in mild or no envenoming. In vipers, it is a determined, quick stabbing bite.

Humans

The rate of increase and the density of the human population in Sri Lanka are high. The density of the population in the years 1881, 1971 and 1995 were 37, 196 and 281 per square km respectively. The estimated mid-year population of Sri Lanka for 1995 is 18.1 million (Registrar General). In the 1981 census 78.50 % of the population was living in rural areas, thus exposing a large population to the risk of snakebite.

Demographic trends

The migration of people between districts has an impact on the incidence and district-wise distribution of snakebite. This is evident in the Accelerated Mahaweli settlement areas where a large urban population was translocated into newly cleared forestlands.

THE OCCUPATIONAL ENVIRONMENT

In Sri Lanka, occupation has a direct relationship to snakebite, as shown by numerous epidemiological studies (de Silva, 1976, 1980, 1981, de Silva & Ranasinghe, 1983, Sawai et al., 1983). The occupation of 45% of the population is agriculture, animal husbandry, forestry, fishing and hunting (Census, 1981). In Sri Lanka, 85% of the circumstances in which snakebite took place were while they engaged directly or indirectly in agricultural activities or related pursuits such as weeding, preparation of fields, harvesting, guarding fields etc. All the known sea snake bites were on fishermen during fishing related activities. It is also not uncommon that some snake charming gypsies and amateur snake hobbyists get bitten by venomous snakes during handling and capture.

THE SOCIAL ENVIRONMENT

The following are some socio-economic factors of the people which have a distinct relation to snakebite and resulting in high mortality.

Housing

In Sri Lanka the majority of farmers live in wattle and daub dwellings with thatched roofs. This is especially so in the dry zone where Bungarus caeruleus is common. The walls and the floor of these wattle and daub houses have many cracks and holes which make ideal niches for rats, snakes and other reptiles; likewise the thatched roofs offer refuge for prey animals. Of over a hundred proven cases of Bungarus caeruleus bites, all occurred in wattle and daub dwellings (de Silva,1987a, 1992, 1997).

Footwear

Seventy four percent of snakebites were inflicted below the knee, while walking on paddy field bunds, tank bunds, foot paths etc. showing the risk of not wearing footwear and of walking on foot paths in the dark or at dusk without a torch (flashlight) (de Silva, 1976, 1980, 1981, de Silva & Ranasinghe, 1983, Sawai et al., 1983). In a study of 62 Hypnale hypnale bites, 85% were inflicted on the feet (Sellahewa, 1997). It was revealed during field interviews with farmers at risk that they were unable to purchase expensive boots, and that anyway wearing boots was impractical while working in paddy fields.

Beliefs and practices

The following beliefs and practices may complicate or even prove fatal in case of snakebite:

a) Resorting to simple home remedies such as applying a cut lime or onion. Some krait envenomed victims too resorted to this home remedy (de Silva, 1992).

b) When bitten by snakes, some do not wish to speak of it, fearing that enemies might "bind the venom" (visha bandeema) resulting in difficulty of curing the condition.

c) The belief that if bitten by snakes on certain inauspicious day, time or place, for example a cemetery, it presaged a poor prognosis (de Silva & Uragoda, 1983).

There has been a general preference for traditional treatment, but this has reversed to some extent following advances in western treatment methods.

MAN-MADE ENVIRONMENT

In Sri Lanka man probably commenced to alter his environment nearly 3 millennia ago. However, the most extensive and permanent clearing of some of the rain, montane and lowland forests was carried out during the past two centuries.

Habitat disturbances/alterations

The rates of deforestation and loss of wildlife habitats in Sri Lanka are some of the highest in South Asia (McNeely et al. 1990). This is mainly due to the high population pressure and clear-felling for agriculture, resulting in the decline of forest cover, accompanied by fragmentation and isolation. With the clearing of forests, scrub jungles and grasslands, most of the fauna, especially mammals and birds, found themselves restricted to these fragmented and isolated forests. Snakes, such as Naja naja, Hypnale hypnale, Daboiarusselii, Bungarus caeruleus etc have adapted themselves for a secretive life in the cleared lands, agricultural fields, compounds and houses, making the "encroaching" human settlers vulnerable to snakebite. Snakes thrive in this environment, as in these cleared settlements, most of the natural predators of snakes, such as wild boar, peafowl, large predatory birds and other natural predators of snakes are rare or absent. On the other hand, due to human activities the prey animals of snakes, such as rats, mice, amphibians, and other reptiles are found in abundance. These could be reasons why the four species, Naja naja, Bungarus caeruleus, Daboia russelii, and Hypnale hypnale which are responsible for nearly 100% of deaths due to snakebite envenoming in Sri Lanka, are common in agricultural fields and near human habitations. A good recent example of this scenario is the Accelerated Mahaweli Development Programme, which is the largest development programme in the country's history. It was started in 1978. Under this programme, nearly 1/3 of the country is to be used for agriculture, settlements and other human activities. Approximately 130,000 ha. (320,000 acres) of mostly forestland were cleared. Of the 140,000 families involved, the majority have already been settled. A high incidence of snakebite is observed in the Mahaweli areas (de Silva & Ranasinghe, 1983, de Silva & Hewage, 1987, Deniyage & de Silva 1989, District Medical Officers, Dehiattakandiya and Embilipitiya, personal communications)

Management of snakebite

In Sri Lanka, the western and the traditional (Ayurveda) systems are the two popular forms of treatment resorted to by snakebite patients.

Shift towards the western system

The ayurveda medical system has played an important role in the medical care of the people of Sri Lanka since the 5th century BC. Before the introduction of western medicine in 1505 AD it was the main health care system in the country. The Government of Sri Lanka by the introduction of the Indigenous Medicine Ordinance in 1941 and the Ayurveda Act of 1961 encouraged and helped the development of ayurveda. There are many traditional systems of snakebite management practiced in the country. However, the most popular method by far is ayurveda (de Silva & Uragoda, 1983). Detailed accounts of the various forms of traditional snakebite treatment in Sri Lanka have been reported by de Silva (1987b, 1993a, 1995) and by de Silva & Uragoda (1983).

During the early days, the western system of snakebite management was "grotesque and hazardous" cauterizing with potassium permanganate, making the patient consume plenty of whiskey etc. Snakebite patients were treated in allopathic hospitals even in the 19th century. In the year, 1879 one snakebite patient had been treated, and in 1880, three cases were admitted (Ceylon Administrative Report, 1880). By 1930 the number had increased to 34, with 2 deaths. However, the advancement of modern medicine, with the introduction of sophisticated management regimes (such as dialysis for kidney failure and ventilation for respiratory failure) as well as the ready availability of antivenom serum has made a tremendous contribution towards effective management of snakebite patients.

There is now increased acceptance of western treatment for snakebite. In 1980, hospital admissions had increased to 2,708 with 36 deaths. By 1995 admissions increased to 25,722, an increase of 850%, and the case fatality rate decreased from 5.4% in 1981 to 1.2 % in 1995. At the same time, admissions to Ayurvedic Hospitals show a decrease.

Conclusion

Sri Lanka could be considered an ideal "field laboratory" to demonstrate that habits of snakes, the environment, socio-economic status of the people and treatment play significant roles in determining the pattern and incidence of snakebite.

Acknowledgements

I wish to thank many friends who helped me with snakes, and joined me in field studies, General hospitals at Anuradhapura, Chilaw, Galnewa, for providing me specimens of offending snakes along with data on snakebite patients. The Permanent Secretary, Ministry of Ayurveda, Statistician, Registrar Generals Office, and the Medical Statistician, Colombo for providing me data on snakebite.

DE SILVA, ANSLEM. 1996. The status of Geochelone elegans in North Western Province of Sri Lanka: Preliminary findings. Proceedings of the International Congress of Chelonian Conservation. SOPTOM. pp. 47-49.

Snakebite and Sri Lanka holds a facination for me due too its high incidence of bites but also the variety of snakes involved in these incidences. Its my hope in the future to actually spend a few weeks there, observing the medical management of snake bite. An interesting article with enough facts to inform the reader who maybe oblivious to the problems but at the same time not being over loaded with statistics.

i am really interested about srilankan snakes and i also have plans of visiting srilanka in future.
is there anybody who can tell me when is the right time to vist the country for a herping trip?
thanx
cjr

Hey you are so coll about this venomous snakes.
Do you have ever visits to Sri Lanka? You know what, I'm a Sri Lankan. And I'm Living in Kandy. Do you have any snakes-bite? Do you have any snakes-bite from Sri Lankan Craits,Vipers, Cobra or any other species. Reply me man.
Creature87.8.13@gmail.com
Wish you have so much livky vith this guys. Goood Bite!

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